The invention relates to hard disk drives and in particular to head suspensions for hard disk drives.
Hard disk drives are used in most personal computers, in mass memory storage systems and in other machines. A typical hard drive includes an enclosure with at least one disk, a spindle motor and an actuator arm with a magnetic recording head. The motor rotates the disk. As the disk rotates, the actuator arm pivots to pass the recording head over the disk surface to read and write data to the disk.
The actuator arm has two ends. One end mounts on a pivot bearing. The other end of the actuator arm supports a head suspension, to which a magnetic head is assembled. Typically, the magnetic head is formed with an air bearing surface, and during operation flies closely over the disk surface to enable data signals to be recorded and read.
Disk rotation creates pressure adjacent to the disk surface, which lifts the suspension and head from the disk surface. The suspension is spring loaded to resist the lifting force and urges the head towards the disk surface. This resistive force is termed the xe2x80x9cgram loadxe2x80x9d. At a desired rotational rate, the gram load and lifting forces balance, allowing the head to float a precise distance from the disk surface.
FIG. 3, for example, shows a known suspension and actuator arm assembly. The assembly has a base plate 52, sometimes referred to as a nut plate assembly, and a suspension 54. The suspension 54 has a circular opening 56. The base plate 52 has a cylindrical hub 58, which extends through the opening 56. Welds attach the base plate 52 to the actuator arm end of the suspension 54, locating the hub in the center of the opening 56. Typically four or six laser welds are used to attach the base plate 52 to the suspension 54.
The suspension 54 is formed from a strip of spring metal having two ends and a bend radius region 55 defined between the ends. The magnetic head is fixed at one end. The other end attaches to the actuator arm 20 by a process known as swaging. During swaging, swage balls of incremental size swage through the hub 58, expanding the hub 58 against the actuator arm 20 to hold the suspension 54 in place with respect to the actuator arm 20. Stresses caused by the swaging process propagate from the base plate via the welds to the bend radius region 55 of the suspension and affect suspension gram load.
The swaging process may inconsistently affect the bend radius region 55, and other parts of the suspension, changing the gram load of the suspension. The magnitude of change in gram load varies, even under closely regulated manufacturing conditions. In some instances, where the desired gram load is in the range of 2-3 grams, swaging may cause gram load changes of xc2xd gram, or more. Ideally, gram load changes should be consistent and predictable during the suspension/actuator arm assembly process.
The gram load directly affects disk drive operation. When, for example, swaging changes the gram load beyond an acceptable range, the head may not record, or read, data properly. To avoid this problem, the suspension is reworked during assembly. Where reworking fails, the whole suspension-actuator arm assembly may have to be de-swaged (removed) and discarded. Optimally, the gram load change will be slight and consistent, and thus the suspension and head assembly will not need to be reworked or discarded. What is desired is a way to minimize inconsistency of gram load changes caused during swaging.
A suspension for a magnetic head includes a first end, a second end and a bending radius region defined between the ends. The bending radius region is configured to preload the suspension. A magnetic head is attached to the first end. Preloading the suspension determines the gram load.
A base plate is welded to the second end of the suspension. The base plate includes a hollow cylindrical hub. The second end of the suspension has an inner periphery defining an opening. The hub inserts through the opening to swage the suspension to an actuator arm of a disk drive. The present invention minimizes stress imposed on the suspension by the swaging process. This minimization of stress, reduces variability and magnitude of gram load changes, which stem from the swaging process.
According to one aspect of the invention, the inner periphery of the suspension includes tabs to minimize force propagation between the base plate and the suspension by isolating forces caused by swaging. According to another aspect of the invention, multiple isolation welds surround the inner periphery to isolate forces caused by the swaging process. The invention can use tabs of uniform length, or varying length. The inner periphery can be generally square, rectangular, or circular in shape to surround the hub. The tabs are preferably parabolic in shape, being rounded, or triangular and pointed. The isolation welds cooperate with the tabs to limit force propagation.